The invention relates to a flow meter or monitor arranged on a conduit section through which a medium to be monitored is to flow. An actuating element extends through an opening in a wall of the conduit section and has a flow pressure plate placed in the flow path of the medium. The actuating element is mounted on a support plate and is deflectable against the force of a spring, with a deflectable outer end projecting into a housing positioned outwardly of the opening in the conduit section. The housing may be detached from the conduit section. The end of the actuating element projecting into the housing is equipped with a permanent magnet that operates a switch, which can be of the reed contact type, in an electrical circuit when the actuating elements is deflected. The switch is surrounded by a protective cover and is accommodated in a through-hole in the housing.
With conventional flow monitors of this type, the actuating element, spring and housing are firmly and inseparably joined together. The actuating element is mounted on the support plate by way of a leaf spring, and the support plate sits firmly in the housing. The support plate has a small opening for the actuating element which extends through an opening in a connecting branch of the conduit section such that the flow pressure plate projects into the flow path of the medium to be monitored in the interior of the conduit. The connection between the housing and the conduit section is achieved through a separable flange joint. The permanent magnet, which actuates the switch by deflection of the actuating element, is located in the inaccessible interior of the housing that is connected with the conduit section. The switch, surrounded by a protective cover and formed as a reed contact, is arranged at the outer end of the housing. For this purpose, the housing, which usually has a circular cross section, has an axial projection which is provided with a through-hole transverse to the axis of the cylindrical housing, for acceptance of a protective cover containing the switch. In order to hold the protective cover and switch in place, a screw perpendicular to the axis of the through-hole is provided. Since the medium to be monitored enters the interior of the housing when the flow monitor is in use, the parts assembled thereat are subject to contamination due to impurities carried by the medium. In particular, magnetizable particles in the medium are attracted by the effect of the permanent magnet, and the accumulation of such particles over a period of time can influence the functional capability of the system. Flow monitors need, therefore, to be cleaned from time to time. Due to the inaccessibility of parts assembled in the housing interior, however, cleaning is practically impossible. An additional disadvantage of conventional flow meters is the considerable effort involved in adjusting the position of the flow pressure plate in the flow path of the medium while assembling the system after cleaning. It has also been shown that the holding fixture for the protective cover and switch in the through-hole of the projection of the housing can damage the reed contact, due to the yielding characteristics of commercially available protective covers.